<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <style>
        body {
            background: url(images/chun1.jpg);
            -webkit-background-size: cover;
            background-size: cover;
        }
    </style>
</head>
<body>
<select name="" id="sele">
    <option value="1">春意绵绵</option>
    <option value="2">夏日炎炎</option>
    <option value="3">秋风瑟瑟</option>
    <option value="4">冬雪皑皑</option>
</select>
</body>
</html>
<script>
    var sele = document.getElementById("sele");  // 下拉列表

    sele.onchange=function () {
//        console.log("11");

          var opts=this.options;
        console.log(opts);

        //        for(var i=0;i<opts.length;i++){
//            if(opts[i].selected){
//
//                if(opts[i].text=="春意绵绵"){
//
//                    document.body.style.backgroundImage="url(images/chun1.jpg)"
//                }
//
//                if(opts[i].text=="夏日炎炎"){
//                    document.body.style.backgroundImage="url(images/xia1.jpg)"
//                }
//            }
//
//
//        }

        switch(this.value){
            case "1":
                document.body.style.backgroundImage="url(images/chun1.jpg)"
                break;
            case "2":
                document.body.style.backgroundImage="url(images/xia1.jpg)"
                break;
        }

    }

</script>